In detectors using the scattered light principle, light pulses of a first wavelength λ1, for example of blue light or near UV light (UV-A) and light pulses of a second wavelength λ2, or example of red light or near infrared light (NIR) are radiated into a common scattered light volume or measuring volume. In some examples, light-emitting diodes are used for radiating in the fight pulses. By means of a photosensor, for example, a photodiode or by means of a further photosensor, scattered radiation intensities which are generated by forward and backward scattering in the scattered light volume are measured. By means of suitable quotient formation from the measured scattered radiation intensities, it is possible to ascertain information regarding the size and nature of the particles detected in the scattered light volume.
Such methods are known, for example, from DE 10 2011 119 431 A1, EP 1 408 469 A2, from EP 1 884 904 A1 and from EP 2 336 993 A1. In EP 1 430 457 A1, a method is described in which a second light-emitting diode is only switched on when the scattered light signal originating from the first light-emitting diode has exceeded a minimum level.